Several problems exist in known valves for remotely controlling fluid flow over a widely-variable range of fluid pressures. Most known valves are constructed so as to puch a cone-shaped plunger end into a hole formed by a valve seat in order to stop fluid flow. If the pressure of the fluid is, for example, 8000 psi, then a relatively high force must be applied to the cone-shaped plunger end by the remote-controlling apparatus in order to close the valve and thereby stop fluid flow. However, when the fluid pressure drops to a low valve, for example 10 psi, the remote-controlling apparatus will still apply the same relatively high force required to close the valve at the upper end of the range of liquid pressures encountered. Thus, the force required to hold off 7990 psi is applied to the cone-shaped plunger and to the valve seat, with the usual result that one or both of these valve components becomes deformed, thereby rendering the valve inoperative.
Another problem in known valves is that the internal volume of the valve varies as the position of the plunger varies. This is an undersirable variable in any system for effecting either a precise flow rate or a precise control of fluid volume passed.
A third problem in known valves is that the internal volume of the valve is so large that it causes mixing of different fluids that are passed through the valve one after the other.